Translator

16 November 2014

Bob Blog

WEATHERGRAM
YOTREPS
Issued 16 November 2014
Bob McDavitt's ideas for sailing around the South Pacific.
Disclaimer: Weather is a mix of pattern and chaos; these ideas are from the
patterned world.

The Atmosphere: The Southern Oscillation Index SOI (30 day running mean)
sums up the weather pattern over the South Pacific as one number. It is
based on the standardised difference in the barometer readings between
Tahiti and Darwin.
It has been negative since July and dived below -10 (Australian units) for
much of September, slightly relaxed for a whole in October, and is now
diving below -10 again. If this index remains below -10 for more than a
month then this will the start of a full blown El Nino episode.

The Ocean
The amount of heat that is being stored in the sea in the Eastern Equatorial
pacific has also increased, as measured by the NINO3.4index.
This indicates that the atmosphere and the ocean are in cahoots.

TROPICAL TOPICS
There are no tropical cyclones around at present: Tropical cyclone activity
has now reduced to just one possible depression area in the Indian Ocean.
Weekly rain maps over the past fortnight show less rain around in the past
week than the previous week.

WEATHER ZONES
SPCZ=South Pacific Convergence zone.
SPCZ has weakened in the past week but is expected to intensify this week
and slowly drift south. It is possible (but models are not yet in
agreement) that a tropical depression may form over Tokelau by Friday 21 Nov
and then move SE across Samoa and near Niue over following few days.

STR= Sub-tropical Ridge
The STR is strong and well defined and north of normal at present (all El
Nino traits).
HIGH between Tonga and NZ at present is expected to travel east along 30/35S
as it peels off to east of 140W by Thursday. Light winds at Minerva from
Monday to Wednesday.
A new HIGH is expected to travel into the Tasman sea around 30S on Mon/Tue
/Wed and then travel east along 30/35S across and to east of NZ on
Thu/Fri/Sat/Sun/Mon 20/21/22/23/24 Nov.

Between the tropics and NZ
At north Minerva:
Light winds in a ridge are expected until Wednesday, then trade winds are
expected to return for the next week or more, good for sailing to NZ.

Over northern NZ:
There is a disturbed westerly flow until Wednesday, and then a slowly
passing High from Thu 20 to Mon 24 Nov, then a passing trough, around Tue
25 Nov , then another passing High from on Wed/Thu 26/27 Nov, and then an
unsettled period with a trough on Fri/sat/ Sun 28/29/30 Nov .
Try and use this to time your arrival in NZ to be in settled weather.